Would be against Ukrainian constitution to have elections under martial law, not to mention impossible to arrange or supervise.

The term dictator is used today to almost always mean that someone wasn't elected to the highest office of their country. Since Zelensky's term expired a while ago, he is a dictator in that literal sense. Arguing that his dictatorship is legal doesn't really matter.

What does matter is that for quite some time now, the average Ukrainian citizen has had no choice about the direction that the country should be going in, especially in regards to whether they should sue for peace right now or how to end the war.

Of course, that's discounting the obvious that bourgeois republics are not really democratic to begin with, but even from the standards of bourgeois democracy, Ukraine fails.